Set fire to a Frenchman's bed (3)
I believe the answer is:
lit
I believe this is a double definition.
'set fire' is the first definition.
(as in lighting a fire)
'frenchman's bed' is the second definition.
('bed' in French)
'to a' acts as a link.
(Other definitions for lit that I've seen before include "landed here" , "Settled" , "Illuminated" , "books etc?" , "Fired" .)